Protective arrangement



Feb. 10, 1931. A 5 FITZ GERALD n 1,792,291

PROTECTIVE ARRANGEMENT Filed Feb. 19, 1929 His AC'Com ey Patented Feb. 10, 19731 UNITED STATES PATENT OFFICE ALAN S. FITZ GERALD, 0F SCHENVECTADYNEW YORK, ASSIGNOR T0 GENERAL ELEC- TRIO COMPANY, A CORPORATION 0F NEW YORK PROTECTIVE ARRANGEMENT Application iled February 1,9, V1929. Serial No. 341,150.

My invention relates to improvements in protective arrangements for electric circuits and more particularly to improvements in. protective arrangements for alternating current circuits wherein discriminating action is obtained by comparison of electric charac-.

pendently of any directly quantitative rela.

tion so as to eliminate discrepancies due to variations in intensity of transmission or reception, attenuation and the like.

My invention will be better understoodv from the following description when considered in connection with the accompanying drawing and its'scope will be pointed out in the appended claims.

The single figure of the accompanying drawing illustrates in a one line diagram, for the sake of clearness, an embodiment of my invention as applied to two points of an alteriiating current circuit such as a power line y conductor l which may extend between a plurality of interconnecte generating and distributin 1 stations, two o which are illusv trated as buses 2 and. Three sections of the line l are shown, extending two from and one between the stations 2 and 3, the last being shown partly by a broken line to give a concept of distance between the stations. For

controlling the circuits of the different sections at the ends thereof, suitable circuit interrupting means such as circuit breakers i and 5 on opposite sides of the bus at station 2 and circuit breakers 6 and onopposite sides of the bus at station 3 ma be provided so that, on the occurrence of a ault on a section the section can be isolated without interrupting continuity of service on sound sections. Allthough my invention is herein illustxated in a sectionalized circuit such as a power line feeder and the like, since it has a particular phase of utility where distance between stations is involved, its application is not se limited as it is alsoadapted to dist criminating protection of parallel lines and 'the like.

In accordance with'my invtution, I provide means such as thermionic apparatus 8 at one point of the circuit for transmitting a carrier wave of a predetermined frequency and for modulating the carrierwave in accordance with an electrical characteristic of; the circuit at the point'. This characteristic of the circuit may be, for example, a current in the circuit or a currentproportional thereto which may be obtained from the output of t suitable transforming means such as a current transformer 9.V The carrier wave may be transmitted through space without wires or as a carrier current over the line conductor 1 from the transmitter 8 to means such as av thermionic receiver 10 located at .another point of the-circuit for`demodulating the modulated carrier wave transmitted by the transi'nitter 8. For controlling the circuit breaker 6 selectively in accordance with the demodulated carrier wave and an electricch'aracteristicof the circuit at the location of the receiver 10, I provide means such as a directional `relay 11 which, as shown, is arranged to beactuated in accordance with the. relative directions of the circuit current at the ends of the section between the statipns 2 and 3, that is, in accordance with the rllative directionsv of thel demodulated earlier current and the current in the circuit l atthe station 3 or a-current proportional theretol as provided by a current transformer 90.

In a similar manner the station 3 is providedl with a transmitter 12 adapted'to transmit a carrier wave having a frequency difiering from that transmitted by the transmitterl 8 and modulated in accordance with the current in. the circuit at station 3, that is by the potential across the secondary. of t e current transformer 90. Also station 2 is provided witn a receiver 13 adapted to demodulate the carrier wave transmitted by the `receiver 12. For controlling the circuit breaker 5, a directional relay 110 is arran ed to be actuated in accordance with the re ative (iirections of the demodulated carrier wave and the current in the secondary of the current transformer 9. Similar apparatus maybe provided for each circuit breaker in the conductor 1 at every station sothat upon the occurrence of a fault in any section the circuit breakers controlling that section are opened and the section is thus isolated.

The transmitters 8 and 12 may be of any suitable type and are herein shown as high frequency devices of a type well known to the art. They include an oscillator element having an oscillator tube 14 and an oscillator circuit 15, the oscillations of which are modulated by a modulator` elementV including a tube 16. The oscillator circuit 15 is coupled to the conductor 1 through` an output coil 17 and the high frequency modulated oscillation or carrier Wave is transmittedin a manner well known to the art over a suitably tuned stop circuit or wave trap 18 and a condenser 19 to the conductor -1. 'The receivers 10 and 13 may be of any suitable t e and are herein shown ashigh frequenc evices of a type well known to the art. liey include a receiving circuit 20 and a rectifier or demodulator tube 21 the output of which may be suitably amplified as is well known to the art. The receiving circuit 20 is coupledto the conductor 1 through an input coil 22 which is energized by the modulated carrier current transmitted over the `condenser 19 and a suitably tuned stop circuit or wave trap 23. The stopcircuits 18 and 23 at the respective 'stations prevent interference between vthe transmitter and receiver at the station by blocking the high frequency oscillation of the transmitter at the station from the receiver at the same station while permitting the passage of the high frequency oscillations from the transmitter 8 or 12 at one A station to the receiver 10 or 13 respectively at the other station. The receivers 10 and 13 are l tuned to the frequencies of the carrier waves transmitted b the transmitters 8 and 12 respectively an in view of inherent variations in line conditions such as length of section, 'impedance and like factors the different circuit elements of the transmitters and receivers may be made adjustable to secure the desired tuning.

For modulating the carrier wave of the oscillator circuit in accordance with the output of the secondary of the current transformer of the station, a secondary circuiq is provided with suitable means such as a resistance 24 which is also included 'in the' grid circuit of the modulator tube 16 so that the potential on the grid will vary in accordance with the current in the circuit 1 at the station. The secondary circuit also includes one of the cooperating windin s 25 of the directional relay at the station. he directional relays 11 and 110 may be of any suitable type examples of which are well known to the art.

In order that the transmitter and receiver at a station may be normally inactive, the secondary circuit may also include suitable when the predetermined current occurs; that 1s, sothat when the predetermined current occurs the relay 27 will pick up and stay up while the current remains at such. predetermined value.

The output or modulated carrier wave of the transmitter at one stationv as rectified or demodulated and amplified, if desired, by the receiver at the adjacent station, is supplied to the cooperating winding 26 of the directional relay at the adjacent station. The

'demodulated carrier current may first be transformed by an intermediate transformer 32 havin a Winding in the plate or output circuit o the receiver and a winding in circuit with the directional relay winding 26. The purpose of the transformer 32 is to obtain better balance between the impedance of the receiver output circuit andthe load circuit which includes the relay winding 26, that is, load impedance.

Although the contacts 33 of the directional to match the tube'impedance with the l relays 11 and 110 in the switch control circuits 34 which include the circuit breaker trip `coils 35 can be arranged normally to be open and remain open on theoccurrence ofv faults outside the protectedy section when the phase of the currents at the ends of the section 2-3 is substantially the same, I preferably arrange .so that the contacts 33 are normally biased closed and remain closed on the occurrence of a fault within the section 2 3 but open on lthe occurrence of a through fault, that is out side of the section 2 3. By so doing proper protection is assured in case of failure of power flow into the section from both ends, freaking of the.line conductor in the protected section and thus interrupting the car- Al`rier channel, if the line conductor is used, or v`failure of the carrier apparatus. `If the directional relay contacts 33 are arranged as shown then I further add, in accordance with my invention, another electroresponsive device such as an overcurrent relay 36 whose -contacts 37 are in series with the contacts 33 in the trip coil circuits and are normally open. In order to avold unnecessary tripping` the relay 36 may be tune delay 1n closing, the time delay being sufficient to allow for the tinul of the directional relay contar-ts 33 opening o so that the circuit breakers 1n a sound ser-tion will not be tripped 1n response to over-current meneer alone unless because of failure ci the dire^- tional relays to open the contacts. ture thus provides an additionai` or back up protection.

Assuming normal line conditions, then iii the overcurrent relays 27 are used, neither the transmitters 8 and l2 nor the receivers l0 and 13 will be operatinjg. Upon the occurrence of an abnormal circuit condition causing a predetermined current in the stations, the relays 27 will operate and thus eiiect the operation of the transmitters and receivers. lf the abnormal circuit condition is due to a through fault, the phase of the currents at the ends of the section 2 3 will be substantially the same and under these conditions the eect of the cooperating windings 25 and 26 of the directional relays will be such as to open the contacts 33. Consequently, the circuit breakers 5 and 6 will not .be opened since their trip coil circuits will be open at the contacts 33 before the overcurrent relays 36 operate to close their.

contacts 37. If, however, the fault is within the section 2'3 and assuming that the system of which the circuit l is a part is such that thefault may be fed from both ends, that is, from stations 2 and 3, then the cooperating windings 25 and 26 exert an eilect tendingito maintain the contacts 33 closed since the currents at ,the stations now diierin phase. If a fault occurs yon the-section 2-3 but power is fed only from one end, say station 2, the winding 26 of the directional relay 110 will not be energized since no carrier current is transmitted from the station 3. Inasmuch as the contacts 33 of the relayllO are biased to the closed position as shown, the circuit breaker- 5 will be tripped in a time dependent on the operation of the overcurrent relay 36 at station 2. Obviously, if for any reason the transmitters or receivers fail to operate or the'carrier channel, conductor l in the illustrated embodiment .of my invention, becomes broken, a fault l.causingan overcurrent cdnditmn will result 1n opening one or both of the circuit brealrers at the ends of the section 2-3 since one or both of the overcurrent relays 36 'will respond and the directional relays will have their contacts 33 closed.' It is to be noted that inasmuch as .the operation of the directional relays is dependent solely upon the relative di-v rections of the currents at the ends of the secv tion 2 3, the fact that the transmitted carrier wavemay not be a true measure of the magnitude et the current at the far end of the s ection, is immaterial. Nor does it matter on the occurrence of a through fault what the direc tion ci the power flow may be.. i

While ll have shown and described my invention in considerable detail, do not desire to be limited to the exact arrangements shown but seek to cover in the appended claims all those modications that fall Within the true spirit and scope of my invention.

This fea Wnat l claim as new and desire to secure by Letters Patent ci the United States, is:

n A protective system for an electric circuit including means at one point of the circuit 'for 'transmitting a carrier wave of a predetermined `reouiency and for modulating the carrier Wave in accordance with a characteristic oi" the circuit at said point, means at another point ofthe `circuit for demodulating said carrier wave and circuit controlling means including a directional relay having cooperating windings connected to be energized respectively in accordance with the demodulated carrier wave and a characteristic of the circuit at said other point.

2. A protective system for an electric cirs cuit including means.l at one point of the circuit for transmitting a carrier Wave of a predetermined frequency and for modulating the carrier wave in laccordance with the circuit current at said point, means at another point of the circuit for demodulating the carrier wave and means for controlling the circuit in accordance with the relative directions othe circuit current at said points including a directional relay having two cooperating windings respectively connected to be energized in accordance with said demodulated carrier Wave and the circuit current at said other point.

3. A'protective system .for an electric circuit including means at one point of the circuit 'for transmitting a carrier Wave of a predetermined -frequency and for modulating the carrier Wave in accordance with the circuit current at said point, means at another point of the circuit for demodulating the carrier wave and means for controllin the circuit in accordance-'With the rrelative irections of the circuitfcurrent at said points and the magnitudeV `of the/'circuit current of one of said points including a directional relay havi having a winding connected to he energized in accordance with the circuit current at said other point.

e. .a protective system for an electric circuit' including means at one point oi the ciruitfor 'transmitting a carrier wave of a predetermined frequency and for modulating the carrier Wave in accordance with the circuitlcurrent at said pointmeans at another point of the circuit for demodulating the car'- rier'wave and means 'or controllin the circuit inaccordance with the relative 'irections of the circuitcurrent at said points and the magnitude.;oifz-1 the circuit curi-ent at one-of said points .including a plurality of series connected means, a directional relay for conn trolling onevof said means having twocooperating windingsv respectively connected to be energized in.- accordance with said demodulated carrier Wave and the circuit current at said other point and a. relay for controlling another of said means having a Winding connected to be energized in ac cordance `With the circuitv Current at 'said other point.

5. A protective system for anaelectric'circuit including means at one point of thecircuit for transmitting a carrier Wave of a predetermined frequency and for modulating the carrier Wave in accordance With the circuit current at said point, means at another point of the 'circuit for demodulating'the carrier Wave, means for controlling the circuit in accordance with the relative directions of the' circuit current at said points and the magni-` tude of the circuit current at one of said points including a switch control circuit, a directional relay having normally closed contacts 4in said circuit and two cooperating windings respectively connected to be energized in accordance with said demodulated Carrier Wave and the circuit current at said other point and a time limit relayhaving norvmally open contacts in said control circuit and a Winding connected to be energized in accordance with the circuit current at said other point.A

6. A protective system for an electric. cir. cuit, including a high frequency transmitter arranged to have its output modulated in accordance with al characteristic of the circuit at one point thereof, a receiver at another point of the circuit tuned to the frequency of said transmitter and circuit controlling' means including a directional relay having a WindingA connected to be energized by said receiver and a cooperating Winding connected to be energized in accordance with a characteristic of the circuit at said other point.l

7. In combination with an electric circuit and circuit controlling means therefor, means for controlling said circuit controlling means cordance with the output of the current transformer at said point, a normally'inactive re. ceiver at another of said points adapted to- 9. A protective system for an alternating 'l current circuit including current transformers associated vvlth the c1rcu1t at separate 4points thereof, transmitting means at one of said points arranged to transmit a carrier current modulated inaccordance with the potential across the secondary of the current'v transformer at said lpolnt, receiving means at another of said-points adapted to demodulate said carrier current` anda directional relay having a Windingconnected to be energized in accordance ,With the demodulated carrier current and a cooperating Winding connected to be energized in-accordance with the output of the current transformer at said other point.

In Witness whereof, I have hereunto set myv hand this 18th day of February, 1929.

ALAN S. FITZ GERALD.

including a directional relay having a Winding connectedto be energized in accordance With the current at one point of the circuitv and a cooperating Winding arranged to be energized in accordance With the current at another point of the circuit, and means for effecting the energization of said cooperating Winding in accordance with the current at said 'other point of the circuit including means for transmitting from said other point a carrier Wave modulated in accordance with the current in the circuit at that point.'

8. A protective arrangementl for anvaltcrnating current circuit including current transformers associated with the circuit at separate points thereof and means for controlling the circuit in accordance with the phase relation between the currents in the circuit at said points including a normally inactive transmitter at one of said points adapted to transmit alcarrier current having a predetermined frequency and modulated in ac- 

